1. Field of the Invention
This invention relates to an electronic control unit for vehicles and more particularly, to the structure of the electronic control unit for vehicles.
2. Description of the Related Art
Electronic control units conventionally located in the vehicle cabin are now more often being installed in the engine compartment of the vehicle in order to reduce cost by shortening the harness for exchanging signals with the unit and also to reduce the effect of noise on other electrical equipment.
Since the engine compartment is a hotter and more humid environment than the cabin, an electronic control unit (hereinafter sometimes referred to simply as an xe2x80x9cunitxe2x80x9d) located there must be highly watertight. Moreover, if the unit houses heat-generating electronic components (heat-generating components), it must also be able to quickly dissipate heat. This led to the development of technologies, such as that taught by Japanese Laid-Open Patent Application Hei 8-169284, for dissipating heat by mounting electronic components directly on a case made from aluminum or other material having good heat dissipation property. In this prior art, however, waterproofing such as by use of an O-ring at the connector portion is necessary because the unit is mounted in the engine compartment.
In another technique developed, the unit and connector are formed as a single integrated plastic case to improve watertightness (waterproof), but the heat generated from heat-generating electronic components cannot be effectively dissipated because no heat sink or other heat-dissipating member is provided.
An attempt has been made to overcome this problem by, as set out in Japanese Patent Publication Hei 6-52831, molding a metal collar integrally into the plastic case and anchoring the collar to a stay etc. by bolts via a metal (aluminum) base.
In the prior art taught by Japanese Patent Publication Hei 6-52831, the unit comprises a plastic case, a metal base and metal collar, each of which has a different coefficient of thermal expansion. As the bolts are liable to loosen by the differences in thermal expansion, a need to ensure more robust mounting strength has been felt.
Therefore, an object of this invention is to provide an electronic control unit mounted in the engine compartment of a vehicle or other high-heat, high-humidity environment that provides excellent heat dissipation when the unit houses heat-generating electronic components, ensures good mounting strength at the fastening portion, particularly in an engine compartment, and also has superior watertightness.
Further, when an electronic control unit of this kind is located in an engine compartment or other high-heat, high-humidity environment, there is a danger that the unit may be affected by the expansion and contraction of the air sealed inside the case when the change in the ambient temperature is great.
Therefore, another object of this invention is to provide an electronic control unit for vehicles that is not affected by changes in ambient temperature when located in the engine compartment of a vehicle or other high-temperature, high-humidity environment.
In order to achieve the objects, there is provided an electronic control unit mounted in an engine compartment of a vehicle, having at least the case body made of plastic, a plurality of the collars each made from metal and each molded into the plastic case body, a base made of metal and having a plurality of the bolt through-holes prepared in the same number of the metal collars such that a bolt passes through each metal collar and one of the holes corresponding thereto, and the heat-generating component mounted on the base. The characteristic features reside in that the outer surface of each of the metal collars that comes in contact with the plastic case body is formed with projections and depressions, each of the metal collars is shaped to be protruded from the end of the plastic case body in a direction of the bolt-through hole, and the plastic case body and the metal base are joined together with the adhesive in such a way that the metal collars and the metal base are fastened together with the bolts to be mounted in the engine compartment.